1. Technical Field
The present invention relates generally to an apparatus and method for estimating the direction of a Radio Frequency (RF) signal and, more particularly, to an apparatus and method that estimate the direction of an RF signal emitted from any transmission device, which is a target, the direction of which is to be estimated, using a directional antenna and an electronic compass.
2. Description of the Related Art
Technology related to the estimation of a direction of an RF signal includes a method based on the strength of signals using an RF reception device, a method using the strengths and phases of signals, a method using the results of a comparison between the strengths or phases of signals at multiple antennas or multiple measurement points, etc.
In fields of radio wave management, national defense, or the like, precise direction-finding performance is required, so an antenna having excellent characteristics for respective bands, a high-sensitive reception device, and a direction-finding algorithm including procedures for correcting various types of measurement data and processing signals must be implemented. In more detail, a typical direction-finding algorithm is configured such that two or more antennas, such as a loop antenna and a dipole antenna, are arranged, and the amplitudes and phases of RF signals received through the respective antennas are extracted, and such that an accurate arrival direction of the RF signals is calculated using a super-resolution algorithm, such as a correlative vector, Multiple Signal Classification (MUSIC), or Maximum Likelihood (ML).
Generally, a typical method is configured such that an analog reception device receives an RF signal and converts the RF signal into a specific Intermediate Frequency (IF) Analog/Digital conversion (ADC) is performed on the IF signal, Fast Fourier Transform (FFT) is performed on a digital signal, and the amplitude and phase of a resulting signal are extracted, and then the above-described direction-finding algorithm is applied. Such a typical method may be regarded as an algorithm using digital signal processing. An algorithm using such digital signal processing is configured such that an exclusive device and software capable of converting, calculating and determining data measured in a detection area must be implemented in detection equipment.
Meanwhile, in illegal signal detection sites requiring, immediate direction estimation via simple measurement in an indoor space, an intuitive direction estimation scheme based on a comparison between the strengths of received signals depending on the pointing direction of an antenna may have advantages from the standpoint of reduction in the complexity of the implementation of a detection system and a user's convenience, compared to the above-described algorithm based on digital signal processing. However, in an indoor environment, the propagation of electromagnetic waves generally has characteristics in which reflective waves obtained through multiple paths coexist due to a wall, a ceiling, a floor, furniture, etc., thus increasing a false detection rate when a direction is estimated.
Related prior technologies include Korean Patent Registration No. 1071202 (entitled “Apparatus and method fix finding the direction of a broadband signal”). The apparatus disclosed in Korean Patent Registration No. 1071202 includes a broadband reception unit, a data extraction unit, a FFT execution unit, and a direction-finding unit. The broadband reception unit receives a broadband signal via an antenna, extracts one or more narrowband signals from the broadband signal, converts the frequency of the extracted narrowband signals, and then outputs IF signals. The data extraction unit extracts Integer/Quadrature (IQ) data from the output IF signals through Analog/Digital (A/D) converters and Programmable Digital Down-converters provided for respective narrowband channels, and outputs the I/Q data. The FFT execution unit performs FFT on the output I/Q data and extracts the amplitudes or phases of the narrowband signals. The direction-finding unit executes a direction-finding algorithm using the extracted amplitudes or phases and simultaneously detects the arrival directions of the one or more narrowband signals. The technology disclosed in Korean Patent Registration No. 1071202 may receive a broadband signal, separate narrowband signals by executing FFT and then detect the directions of the narrowband signals, and may simultaneously detect directions regardless of the number of narrowband signals even if a limited number of antennas are used. The invention disclosed in Korean Patent Registration No. 1071202 is not intended to provide a portable direction-finding apparatus, and it is technology that focuses on direction-finding based on the execution of a direction-finding algorithm using two or more antennas and based on a data correction procedure or the like. Further, the invention disclosed in Korean Patent Registration No. 1071202 requires the implementation of hardware and software only for direction-finding required to extract I/Q data from IF signals and execute a direction-finding algorithm so as to realize precise direction-finding performance.
Another prior technology includes Korean Patent Registration No. 1174443 (entitled “Location determination apparatus”). The apparatus disclosed in Korean Patent Registration No. 1174443 includes an RF transmission unit and a portable location determination device. The RF transmission unit is installed in a vehicle and configured to transmit a signal. The portable location determination device includes a directional receiving antenna for receiving a signal from the vehicle which is a target, the location of which is to be determined, in a wireless manner, a reception strength detection unit for measuring the strength of the signal received through the directional receiving antenna, a geomagnetic sensor for detecting a direction in which the directional receiving antenna is disposed, and a display unit for displaying the strength of the signal measured by the reception strength detection unit. The portable location determination device is configured such that the display unit displays the direction in which the directional receiving antenna is disposed and which is detected by the geomagnetic sensor, together with the strength of the signal measured by the reception strength detection unit. Further, when the number of vehicles is two or more, and the directional receiving antenna receives a signal from any one of the two or more vehicles, information required to identify a target is further received, and the display unit displays information required to identify the vehicle together with the strength of the signal measured by the reception strength detection unit. In accordance with the invention disclosed in Korean Patent Registration No. 1174443, the location of an object requiring location determination may be determined using separate equipment or a mobile communication terminal. Such an invention disclosed in Korean Patent Registration No. 1174443 is intended to determine a location while performing radio communication with a transmitter previously installed in each vehicle or the like. Therefore, the invention premises radio communication between the target and the location determination device, thus enabling a direction to be detected only in a specific communication frequency band.